A new type of second-order phase transition derived from Devonshire's theory of ferroelectrics

Including external fields Devonshire's theory of ferroelectric phase transitions leads to a type of second-order transitions for which the order parameter is different from zero below and aboveT _c . Although in a certain limiting case the order parameter becomes zero aboveT _c the resulting theory is nevertheless different from the usual Landau-theory suggesting the existence of different types of systems undergoing second-order phase transitions.